Interesting 26

What is interesting about the number 26?

Every integer is interesting

26 is the largest integer that is more than 3 times of its digit sum 26 is the smallest integer that can be written as the sum of two positive perfect squares 26 is the only two-digit integer with 4 factors 26 is the smallest integer that is 1 smaller than a perfect cube and 1 larger than a perfect square

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1 solution

Sean Sullivan
Jul 19, 2015

Perfect cubes under 27 27 are just 8 8 and 1 1 , the 4 4 th answer claims 27 27 the lowest number 1 1 less than a cube and 1 1 more than a square. Simply showing 6 = 2 3 6=2*3 is not a perfect square is enough to show this as the right answer

EDIT:

The other solutions are incorrect because:

All numbers of the form n = p q n=pq or n = p 3 n=p^{3} for primes p p and \q) have 4 4 factors, taking p = 3 p=3 and q = 5 q=5 yields n = 15 n=15 has 4 4 factors and also has two digits meaning 26 26 is not the only two-digit number with 4 4 factors

Taking the two smallest square numbers and adding them together will give the smallest sum of two positive perfect squares. 1 2 + 2 2 = 5 1^{2}+2^{2}=5 so 26 26 is not the smallest number with these qualifications

Reversing the digits of 26 26 is 62 62 , as three times its digits sum will be the same for these numbers and 62 > 26 62>26 we see 62 62 will also be greater than three times its digits sum. Because 62 > 26 62>26 , 26 26 is not the largest number to meet this qualification

For completeness, you should also explain why the other options are not correct.

Calvin Lin Staff - 5 years, 11 months ago

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